Macroscopic samples, of matter

Our world can be studied at different levels of magnification. At the macroscopic level, matter is large enough to be seen, measured, and handled. A handful of sand and a glass of water are macroscopic samples of matter. At the micro-scopic level, physical structure is so fine that it can be seen only with a microscope. A biological cell is microscopic, as is the detail on a dragonfly s wing. Beyond the microscopic level is the submicroscopic—the realm of atoms and molecules and an important focus of chemistry. 

Enormous numbers of microwave photons are needed to warm macroscopic samples of matter. A portion of soup containing 252 g of water is heated in a microwave oven from... 

This paper is concerned with the properties and dynamical propensities of many-body Van der Waals clusters, species too large to be treated quantum mechanically as a single molecule, yet far too small to take on the properties of a macroscopic sample of matter. The work was motivated by a desire to understand what happens to the familiar macroscopic property known as a "phase transition" when a system becomes "finite", on a molecular scale. More particularly, we wish to learn how the nature of the intermolec-ular forces between the component particles affect these properties. 

We can describe some forms of matter by observation with the naked eye. These macroscopic samples of matter include a huge range of sizes, varying from mountains, rocky cliffs, huge boulders, and all sizes of rocks and stone to gravel and tiny grains of sand. Geologists often study matter at this level. 

Figure 2.11 Homogeneous pure substances and mixtures. The terms homogeneous and heterogeneous refer to macroscopic samples of matter. They are a reference to the macroscopic appearance of the substance. Homogeneous matter may be either a pure substance or a mixture. 

Starting with Dalton, chemists have recognized the importance of relative munbers of atoms, as in the statement that two hydrogen atoms and one oxygen atom combine to form one molecule of water. Yet it is physically impossible to count every atom in a macroscopic sample of matter. Instead, some other measurement must be employed, which requires a relationship between the measured quantity, usually mass, and some known, but imcoimtable, niunber of atoms. Consider a practical example of mass substituting for a desired mun-ber of items. Suppose you want to nail down new floorboards on the deck of a mountain cabin, and you have calculated how many nails you will need. If you have an idea of how many nails there are in a poimd, then you can buy the iiails by the pound. 

Matter is anything that has mass and occupies space. A sample of matter can contain a single substance or any number of different substances. As already described, the building blocks of most substances are molecules, which in turn are composed of atoms. It is convenient to classify samples of matter according to the complexity of their composition, both at the atomic level and at the macroscopic level. 

This definition of entropy shows its exact relationship to probability. However, it is not useful in a practical sense for the typical types of samples used by chemists, because these samples contain so many components. For example, a mole of gas contains 6.022 X 1023 individual particles. In addition, according to one estimate, describing the positions and velocities of this mole of particles would require a stack of paper 10 light years tall—and this description would apply for only an instant. Clearly, we cannot deal directly with this definition of entropy for typical-sized samples. We must find a way to connect entropy to the macroscopic properties of matter. To do so, we will consider an ideal gas that expands isothermally from volume V] to volume 2V] (see Fig. 10.10). 

All matter is made of particles. The type and arrangement of the particles in a sample of matter determine the properties of the matter. Most of the matter you encounter is in one of three states of matter solid, liquid, or gas. Figure 2 illustrates water in each of these three states at the macroscopic and microscopic levels. Macroscopic refers to what you see with the unaided eye. In this text, microscopic refers to what you would see if you could see individual atoms. 

The large clusters are essentially small particles of bulk matter. Their properties vary little with size. They differ from ordinary bulk matter primarily in having large surface areas and enough curvature of those surfaces to make their equilibrium vapor pressures and other related properties a bit different from those of macroscopic samples of the same materials. 

System and Surroundings We tend to consider (material) systems as strongly simplified, often idealized, parts of the natural world around us in which we have a special interest. For example, we can be interested in a mbber ball, a block of wood, a raindrop, the air in a room, a solution in a test tube, a soap bubble, a ray of light, or a protein molecule. We assume that systems can appear in various (physical) states, where the word state means a momentary specific condition of a sample of matter determined by macroscopic characteristics. States can differ qualitatively due to characteristics such as state of aggregation or crystal stmcture or quantitatively in the values of suitably chosen quantities such as pressure, temperature, and amount of substance. 

Samples of matter large enough to be seen, felt, and handled— and thus lai e enough for ordinary laboratory experiments— are called macroscopic samples. In contrast, microscopic samples are so small that they have to be viewed with the aid of a microscope. The structure of matter that really interests chemists, however, is at the nanoscopic level. Our senses have limited access into this small world of structure, although new kinds of instruments are beginning to change this condition (Figure 2.1). 

H. Mao and M. A. Hillmyer, "Macroscopic Samples of Polystyrene with Ordered Three-Dimensional Nanochannels, Soft Matter. 2, 57-59 (2006]. 

Traditionally a phase is defined in thermodynamic terms as a state of matter that is uniform throughout, not only in chemical composition, but also in physical state. In other words, a phase consists of a homogeneous, macroscopic volume of matter, separated by well-defined surfaces of negligible influence on the phase properties. Domains in a sample, which differ in composition or physical states, are considered different phases. The basic elements of the phases are the atoms and molecules as discussed in Sect. 1.1.3. 

The units, Al atoms, are correct. The answer makes sense because the number of atonrs in any macroscopic-sized sample of matter should be very large. 

Most of the time, chemists work with macroscopic samples in the laboratory, but they imagine what happens at the particulate level while they do so. Biologists frequently work with microscopic samples, but they also think about the particulate-level behavior of their samples to supplement their understanding of what they see through the microscope. By understanding and directing the behavior of particles, the chemist and biologist control the macroscopic behavior of matter. 

Identify the following samples of matter as macroscopic, microscopic, or particulate (a) a human skin cell (b) a sugar mol-... 

Macroscopic c. Microscopic a, e. Particulate b, d. 3. An advantage is that understanding the behavior of particles allows us to predict the macroscopic behavior of samples of matter made from those particles. Chemists can then design particles to exhibit the macrosa ic characteristics desired, as seen with drug design and synthesis, for example. 5. Your illustration should resemble the particulate view in Figure 2.5. 7. A dense gas that is concen-... 

Since solids do not exist as truly infinite systems, there are issues related to their temiination (i.e. surfaces). However, in most cases, the existence of a surface does not strongly affect the properties of the crystal as a whole. The number of atoms in the interior of a cluster scale as the cube of the size of the specimen while the number of surface atoms scale as the square of the size of the specimen. For a sample of macroscopic size, the number of interior atoms vastly exceeds the number of atoms at the surface. On the other hand, there are interesting properties of the surface of condensed matter systems that have no analogue in atomic or molecular systems. For example, electronic states can exist that trap electrons at the interface between a solid and the vacuum [1]. 

In the previous sections we have described the interaction of the electromagnetic field with matter, that is, tlie way the material is affected by the presence of the field. But there is a second, reciprocal perspective the excitation of the material by the electromagnetic field generates a dipole (polarization) where none existed previously. Over a sample of finite size this dipole is macroscopic, and serves as a new source tenu in Maxwell s equations. For weak fields, the source tenu, P, is linear in the field strength. Thus,... 

The thermodynamic state is therefore considered equivalent to specification of the complete set of independent intensive properties 7 1 R2, Rn. The fact that state can be specified without reference to extensive properties is a direct consequence of the macroscopic character of the thermodynamic system, for once this character is established, we can safely assume that system size does not matter except as a trivial overall scale factor. For example, it is of no thermodynamic consequence whether we choose a cup-full or a bucket-full as sample size for a thermodynamic investigation of the normal boiling-point state of water, because thermodynamic properties of the two systems are trivially related. 

There exists an alternative explanation. Egami, Maeda et al. 85) introduced different kinds of defects of n , p and t type to characterize the glassy state of matter. Defects of n and p-type correspond to negative and positive density fluctuations while the defects of x-type are the shear defects which do not change the specific volume of the system. Different defects through which the total free volume of a sample is distributed affect different properties. If curing at different Tcur<. leads to polymers with different defect ratios, the differences in the macroscopic behaviour can be explained. 

In theory, the previous advantages could make miniaturization a panacea in practice, however, they do not. Thus, when a system is scaled down, some characteristics such as lengths, areas and volume ratios can differ so markedly from those of macroscopic systems as to affect the development of the process concerned. The new behaviour will be dominated by material confinement in small structures, a large interfacial volume fraction and various unique properties, phenomena and processes. In fact, many current theories of matter at the microscale level have critical gaps for nanometer dimensions and fail to describe the new phenomena observed at the nanoscale level accurately [66]. Also, scaling-down can be problematic with samples containing low analyte concentrations as their determination will require larger amounts of sample. 

The LVFS has been successfully deployed on 11 cruises in the Atlantic and Pacific Oceans. Analyses of the samples have made known the distributions of over 20 elements and have documented the importance of particulate organic matter as a complexing and ion-exchange agent. Furthermore, the results have demonstrated that macroscopic aggregates (fecal matter)... 

If not for the fact that most solids condense into periodic crystal structures, the field of condensed matter would not exist. The periodicity makes it possible to perform calculations for only one piece of the bulk matter (called a unit cell, see Fig.(1.2), or if you study properties with periodicities longer than a unit cell supercell), which then yields the solution for the whole sample. In a macroscopic sample you have both surface atoms and bulk atoms. The number of surface atoms are of the order of N, or about 1 out of 108 in a macroscopic sample. They are therefore neglected in the calculation of bulk properties, and only included if you want to study specifically some property with regard to surfaces. There are also always defects and impurities present in a sample, but these are, although interesting, neglected in the following discussion (and furthermore for the rest of... 

Matter can be broadly classified into three types—elements, compounds, and mixtures. An element is the simplest type of matter with unique physical and chemical properties. An element consists of only one kind of atom. Therefore, it cannot be broken down into a simpler type of matter by any physical or chemical methods. An element is one kind of pure substance (or just substance), matter whose composition is fixed. Each element has a name, such as silicon, oxygen, or copper. A sample of silicon contains only silicon atoms. A key point to remember is that the macroscopic properties of a piece of silicon, such as color, density, and combustibility, are different from those of a piece of copper because silicon atoms are different from copper atoms in other words, each element is unique because the properties of its atoms are unique. 

Of the three states of matter, the liquid is the least understood at the molecular level. Because of the randomness of the particles in a gas, any region of the sample is virtually identical to any other. As you ll see in Section 12.6, different regions of a crystalline solid are identical because of the orderliness of the particles. Liquids, however, have a combination of these attributes that changes continually a region that is orderly one moment becomes random the next, and vice versa. Despite this complexity at the molecular level, the macroscopic properties of liquids are well understood. In this section, we discuss three liquid properties— surface tension, capillarity, and viscosity. 

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